A known example of a wave gear unit is a wave gear unit having an input shaft and a pair of input bearings supporting the input shaft, the axial position of the input shaft being defined by the input bearings. Wave gear units with input bearings having this structure are proposed in Patent Documents 1 to 3.
A wave gear unit with input bearings has a first unit end plate for rotatably supporting one first shaft end of an input shaft via a first input bearing, and a second unit endplate for rotatably supporting another second shaft end of the input shaft via a second input bearing. A wave gear mechanism is incorporated between the first and second unit endplates. The wave gear mechanism has a wave generator which rotates integrally with the input shaft, a flexible externally toothed gear made to flex into a non-circular shape by the wave generator, and a rigid internally toothed gear partially meshed with the flexible externally toothed gear. The flexible externally toothed gear and the rigid internally toothed gear are disposed so as to be capable of rotating relatively via a unit bearing (a crossed roller bearing).
To reduce the weight of the wave gear unit with input bearings, improvements are made for reducing the weight of both the wave gear mechanism and the crossed roller bearing. In Patent Documents 1 to 3, the rigid internally toothed gear is a composite member composed of a gear main body member of a lightweight material and a teeth formation member of an iron-based material. The inner and outer rings of the crossed roller bearing are composite members in which the main body portions are formed from a lightweight material, and the trajectory surface formation portions are formed from an iron-based material.